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晶粒尺寸对低强度材料疲劳裂纹扩展的影响规律,业已清楚,但为数不多有关高强度钢的类似工作,却出现矛盾结果。本文使用不同晶粒尺寸和经不同温度回火,即具有不同强度水平的65Mn 钢试样,进行疲劳裂纹扩展试验。研究结果表明,随奥氏体晶粒粗化,两种强度水平试样,都具有降低 dα/dN,增加△K_(th)的相同规律,且△K_(th)、△K_T 与d~(1/2)存在线性关系,但高强度试样对晶粒尺寸影响的敏感性比低强度材料低。作者通过对循环塑性区尺寸 r_y~c 的估算,分析了组织因素尺寸■的含义,并指出马氏体对奥氏体的分割作用降低了■值。高温回火使马氏体界面消失,恢复奥氏体晶界的主导作用,是不同强度材料在晶粒尺寸影响敏感性差别的主要原因。
The effect of grain size on the fatigue crack growth of low-strength materials is well understood, but one of the few similar work on high-strength steels has resulted in conflicting results. In this paper, different grain sizes and different temperature tempering, that is, with different strength levels of 65Mn steel samples for fatigue crack growth test. The results show that with the austenite grain coarsening, the specimens with the two strength levels have the same regularity of decreasing dα / dN and increasing △ K_ (th), and △ K_ (th), △ K_T and d ~ 1/2), but the sensitivity of high strength specimens to grain size is lower than that of low strength materials. By estimating the size of the cyclic plastic zone r_y ~ c, the author analyzed the meaning of the size of the tissue factor ■ and pointed out that the martensite has a reduced ■ value for the segregation of austenite. High-temperature tempering causes the martensite interface to disappear and the dominant effect of restoring the austenite grain boundary is the main reason for the difference in the sensitivity of different strength materials in the grain size.